1. Field of Invention
This invention relates to toners, developers containing the toners, and a method of forming images with the developers utilizing a magnetic brush development system. More in particular, the invention relates to toners and developers having carefully controlled properties to provide superior print quality when used in developing electrostatic images with a magnetic brush development system.
2. Description of Related Art
U.S. Pat. No. 5,545,501 describes an electrostatographic developer composition comprising carrier particles and toner particles with a toner particle size distribution having a volume average particle size (T) such that 4 .mu.m.ltoreq.T.ltoreq.12 .mu.m and an average charge (absolute value) pro diameter in femtocoulomb/10 .mu.m (C.sub.T) after triboelectric contact with said carrier particles such that 1 fC/10 .mu.m.ltoreq.C.sub.T.ltoreq.10 fC/10 .mu.m characterized in that (i) said carrier particles have a saturation magnetization value, M.sub.sat, expressed in Tesla (T) such that M.sub.sat.gtoreq.0.30 T, (ii) said carrier particles have a volume average particle size (C.sub.avg) such that 30 .mu.m.ltoreq.C.sub.avg.ltoreq.60 .mu.m, (iii) said volume based particle size distribution of said carrier particles has at least 90% of the particles having a particle diameter C such that 0.5 C.sub.avg.ltoreq.C.ltoreq.2 C.sub.avg, (iv) said volume based particles size distribution of said carrier particles comprises less than b % particles smaller than 25 .mu.m wherein b=0.35.times.(M.sub.sat).sup.2.times.P with M.sub.sat : saturation magnetization value, M.sub.sat, expressed in T and P: the maximal field strength of the magnetic developing pole expressed in kA/m, and (v) said carrier particles comprise a core particle coated with a resin coating in an amount (RC) such that 0.2% w/w.ltoreq.RC.ltoreq.2% w/w. See the Abstract. This patent describes that such developer achieves images of offset-quality in systems in which a latent image is developed with a fine hair magnetic brush. See column 4, lines 7-17 in said patent.
XEIKON NV currently supplies the market with developers from AGFA for magnetic brush development systems. These developers are comprised of toner and carrier particles. The toner is believed to be comprised of pigments and two polyesters, a propoxylated bisphenol-A, hexanedioic acid, isophthalic acid polyester and an ethoxylated bisphenol-A ethylene glycol, isophthalic acid, terephthalic acid polyester, while the carrier is believed to be comprised of an iron-zinc-copper oxide core coated with a crosslinked siloxane. However, such developers suffer from lower triboelectric stability and image quality stability, and insufficient color gamut.
What is still desired is a set of developers comprised of toners and carriers that possess a combination of properties such that when used to develop a latent image on the surface of a photoreceptor with a magnetic brush, the color image produced in this xerographic manner exhibits a very high quality, improved in most properties over conventional magnetic brush toners and developers.